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TZA3041

Gigabit Ethernet/Fibre Channel laser drivers

Philips Electronics 

Philips Semiconductors

Gigabit Ethernet/Fibre Channel laser

drivers

Product specification

TZA3041AHL; TZA3041BHL;

TZA3041U

For ECL signals (negative and referenced to ground), the

inputs should be AC-coupled to the signal source.

If AC-coupling is applied, a constant input signal (either

LOW or HIGH) will cause the device to be in an undefined

state. To avoid this, it is recommended to apply a slight

offset to the input stage. The applied offset must be higher

than the specified value in Chapter “Characteristics”, but

much lower than the applied input voltage swing.

The RF path is fully differential and contains a differential

preamplifier and a main amplifier. The main amplifier is

able to operate at the large peak currents required at the

output laser driver stage and is insensitive to supply

voltage variations. The output signal from the main

amplifier drives a current switch which supplies a

guaranteed maximum modulation current of 60 mA to

pins LA and LAQ (see Fig.6). The BIAS pin outputs a

guaranteed maximum DC bias current of up to 90 mA for

adjusting the optical laser output to a level above its light

emitting threshold (see Fig.7).

handbook, halfpage

LA LAQ

Automatic laser control

A laser with a Monitor PhotoDiode (MPD) is required for

the laser control circuit (see application diagrams

Figs 18 and 19).

The MPD current is proportional to the laser emission and

is applied to pin MONIN. The MPD current range is

100 to 1000 µA (p-p). The input buffer is optimized to cope

with an MPD capacitance of up to 50 pF. To prevent the

input buffer from oscillating if the MPD capacitance is low,

the capacitance should be increased to the minimum value

specified in Chapter “Characteristics”, by connecting a

capacitor between pin MONIN and VCC(G).

DC reference currents are applied to pins ONE and ZERO

to set the MPD reference levels for laser HIGH and laser

LOW respectively. This is adequately achieved by using

resistors to connect VCC(R) to pins ONE and ZERO

(see Fig.8), however, current DACs can also be used. The

voltages on pins ONE and ZERO are held at a constant

level of 1.5 V below VCC(R). The reference current applied

to pin ONE is internally multiplied by 16 and the reference

current flowing into pin ZERO is internally multiplied by 4.

The accuracy of the VCC(R) − 1.5 V voltage at pins ONE

and ZERO is described in Section “Accuracy of voltage on

inputs: ONE, ZERO, ALARMLO, ALARMHI”.

TR

TRn

ALS

GND

MGS906

Fig.6 LA and LAQ outputs.

handbook, halfpage VCC(R)

30 kΩ

ONE, ZERO, ALARMLO, ALARMHI

handbook, halfpage

BIAS

TR

TRn

ALS

GND

MGS907

Fig.7 Laser driver bias current output circuit.

2002 Aug 13

50 µA

GND

MGS908

Fig.8 ONE, ZERO, ALARMLO and ALARMHI

inputs.

7

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